I have a question about C:B ratios for metered propane combustions canons. I know from reading the test results at http://www.burntlatke.com that the optimal C:B ratio for a fixed size combustion chamber is ~.7 or .8 :1. My question is, If you added a larger chamber to a gun that was already at that .7 or .8:1 ratio, will it slow the velocity of the spud? My guess is it will do little for the velocity of the spud, but make a louder bang. I realize lengthening the barrel at this point would increase velocity.

If this question has been answered, I apologize. I have tried looking all over the net for a test with a fixed size barrel and varying sizes of combustion chambers.

huse_spud wrote:umm... if you look at the graphs at burntlatke you can answer your own question.

but i think he calls his preffered ratios the most effiecient and not necessarily the most powerful.

different barrel and chamber diameters and launcher configuration can also make a difference too.

Thank you, unfortunately I was afraid this was going to be the kind of response I would get. Maybe I am not being clear enough. The graphs on burntlatke represent how to get the most out of a fixed size chamber, or transferring as much energy to the projectile as possible before friction from excess barrel slows it down. However if I were to add a large chamber (more energy) to the barrel, I do believe that the projectile would not be slowed. However the extra energy would not be transferred to the projectile because of the lack of extra barrel length. The extra energy would dissipate as sound. I realize my theory may be incorrect due to the chemistry and physics of combustion, i.e. optimal combustion pressure may not be reached before the projectile leaves the barrel.

Yes, a larger chamber (to a degree) will give you more power.The 'degree' being best illusrated by the salt-mine scenario: the gasses might take 15 seconds to burn, by which time the potato has long ago left the barrel. The pressure in the barrel during it's time there was pretty low, so the projectile never got much velocity.